Exploitation of petiole, nodal segment, bulbil and tuber anatomy for species identification in Dioscorea Linn. species from Oyo and Ekiti states- southwestern Nigeria

Abstract

Herb sellers and Traditional Medical Practitioners often substitute D. hirtiflora, cultivars of D. bulbifera and D. dumetorum with closely related cultivars within species during herbal preparations. This practice, which may be as a result of mis-identification, may be very injurious to users of herbal products. The present study investigated anatomical characters of three wild and edible species of Dioscorea used in ethnomedicine in Southwestern Nigeria with a view to aiding species identification. Thin sections of the median petiole and nodal segments were prepared using free hand sectioning. Bulbils and tubers stored in 50% ethanol were sectioned at 5 μm with the aid of a sledge microtome. Sections were stained in Safranin O solution for 2-10 min while sections from bulbils of D. hirtiflora were counter stained with toluidine for 1 min and mounted with glycerol. All slides were examined under the light microscope at x100 and x400 magnifications and photos were taken using digital camera mounted on Zenith Ultra-500 A light microscope. Petiole and nodal segments anatomy showed six and nine vascular bundles, respectively in D. hirtiflora, whereas eight and eleven bundles were observed in D. dumetorum and D. bulbifera. Petioles of D. hirtiflora and D. dumetorum were profusely surrounded with stellate and simple unicellular trichomes. Parenchyma cells in wild D. dumetorum were beaded, while they were not in the edible cultivar. Generally, scattered vascular bundles, layers of collenchymas cells, and dilated parenchyma cells filled with tannins were observed in the bulbils/tubers of all species. Anatomical characters in the selected Dioscorea species are taxonomically significant for species identification and could serve as diagnostic taxonomic tools for their standardization.

Keywords: Anatomy, Dioscorea spp., Identification, Medicinal application